The invention relates to a heat exchanger.
Heat exchangers for air-conditioning systems using R134a as refrigerant comprise a heat exchanger network made up of flat tubes and corrugation fins, as well as collection tubes which are arranged on both sides of the network and are preferably circular in cross section, as are known from DE-A 42 38 853 in the name of the present Applicant. Designs of this type have a sufficient strength to cope with the pressures which occur in a condenser. However, with more recent refrigerants, such as CO2, the pressures are considerably higher and the conventional designs of heat exchangers are no longer able to cope with such pressures. Therefore, in the extruded collection tube of increased wall thickness disclosed by WO 98/51983, it has been proposed that a collection tube comprise four flow passages of circular cross section arranged next to one another. An extruded collection tube of this type is expensive to produce, on account of the tooling required. Another type of collection tube for high internal pressures has been proposed in DE-A 199 06 289, in which the collection tube is assembled from two or three extruded or pressed parts and has two longitudinal passages which are circular in cross section. If this known collection tube is composed of extruded parts, the relatively high tooling costs are disadvantageous; if the known collection tube is composed of pressed parts, the shape appears to be incomplete, i.e. inadequately adapted to the expected stresses caused by the high internal pressure.
A further design of the header of a conventional condenser has been disclosed by U.S. Pat. No. 5,172,761. The condenser has flat tubes which are received in slot-like openings in a substantially planar but profiled tube plate. A substantially planar but also profiled cover part is connected to the tube plate. The tube plate and cover form individual chambers which are divided by transverse walls and in which the refrigerant flows or is diverted. Although the tube plate and cover are brazed to one another in the region of the tubes by means of inwardly facing stamped formations, this shape of a header does not appear suitable for relatively high pressures, as occur in particular in a CO2 refrigerant circuit.